This is pretty easy depending on what you want and how much security
If you are using a daabase and want the user to be able to register and then have instant access you can do it like this
create a form the lets the user choose a user name and password you can add feature like to see if those name are taken and so
now on the pages you want secure just add a HTTP AUTH Header and use cookies to pass the user name and password to each of the secure pages use a log out button to delete the cookie so that way they have to relog
this is a simple login
Hope this helps
